1. Field of the Invention
The present invention relates to a bodily state detection apparatus that detects the bodily state of the subject person by taking pictures of the retinal reflection obtained with the so-called coaxial illumination directed to that person. More particularly, the invention relates to a physiological or psychological state detection apparatus that detects primarily the alertness or the tenseness of the subject person based on the pictures taken of that person, practiced illustratively as an apparatus that detects the drowsiness or the psychological state of a vehicle driver.
2. Description of the Related Art
Conventional apparatuses offering the above-stated features include the organic state detection apparatus disclosed in Japanese Patent Laid-open Application No. Sho 63-217500 and the driver drowsiness prevention apparatus disclosed in Japanese Patent Publication No. Hei 3-14655. These apparatuses each have transceiver means mounted on the eyeglass frame worn by the subject person. In operation, the apparatus senses the reflection from the eyelids or from the corneas to see if the eyelids are open or closed, thereby detecting the bodily state of the subject person. A major disadvantage of this type of apparatuses is the annoying need for the subject person to wear the eyeglass frame.
There exist other conventional apparatuses capable of detecting the bodily state on a noncontact basis without requiring the subject person to wear any detectors that would hamper the proper work or operation performed by that person. One such apparatus is the eye position recognition apparatus disclosed in Japanese Patent Laid-open Application No. Sho 60-158303. The disclosed apparatus comprises a camera that takes face pictures of the subject person, and means for detecting pupil and eyelid movements through the image processing based on the pictures taken. FIG. 1 is a schematic view of the disclosed apparatus used as a drowsiness detection apparatus. In FIG. 1, reference numeral 1 is a subject person; 2 is an infrared LED which illuminates the subject person 1 and which has a center illumination wavelength of 860 nm; 3 is a CCD camera that converts face pictures of the subject person 1 into electrical signals; 10 is a pickup image memory that stores temporarily the output data of the CCD camera 3; 20 is a feature point extraction circuit that extracts the pupil movement from the data in the pickup image memory 10; and 40 is a drowsiness judgement circuit that checks to see if the subject person is drowsy by detecting the eyelid movement from the data furnished by the feature point extraction circuit 20.
In operation, the infrared LED 2 illuminates the subject person 1. The image of the subject person 1 is input to the CCD camera 3 so positioned as to take pictures of a predetermined area including the face of the subject person 1. The pickup input image memory 10 receives and accommodates the output data from the CCD camera 3. The feature point extraction circuit 20 extracts the pupil position, eye position, face orientation and other features through image processing based on the data from the pickup input image memory 10. When, say, the pupil movement is extracted by the feature point extraction circuit 20, the drowsiness judgement circuit 40 detects the apparent presence or absence of the pupils. If the pupils are apparently absent for a predetermined period of time, the drowsiness judgement circuit 40 determines that the subject person 1 is being drowsy.
FIG. 2 is a view of an infrared image used by the conventional apparatus of FIG. 1. In FIG. 2, reference numeral 4 is the iris, 5 is the sclera, 6 is the pupil, and 7 is the face surface. In the image thus obtained, the face surface 7 appears a little dark, the sclera 5 darker than the face surface 7, the iris 4 darker than the sclera 5, and the pupil 6 still darker than the iris 4.
One disadvantage of the bodily state detection apparatus structured as outlined above is that it needs complicated image processing whereby the eyelid movement is to be detected. Specifically, the obtained image is subjected to filter computation and then to edge detection. The shape of the detected edge is used to perform a pattern recognition process by which to find the circular arcs representing the eyelids. With the eyelid position determined, the eyelid shape is calculated in further detail. During edge detection, the circular arcs are hard to find if the edge is not detected smoothly due to the presence of noise or other disturbances. All this contributes to making the image processing a time-consuming and complicated procedure.
Meanwhile, there has been proposed a system that detects the eye position through very simple image processing such as binary processing. That system comprises a coaxial illumination device that illuminates the face surface of the subject person to let pictures of the retinal reflection be taken for the simplified image processing, as discussed in "Prototype of Gaze Direction Detection Apparatus Permitting Pupil Data Extraction and Head Movement" (Technical Report of the Institute of Electronics, Information and Communication Engineers of Japan; D-II, Vol. J76-D-II, No. 3). The coaxial illumination device is a device wherein the optical axis of the camera and the direction of illumination coincide with each other.